Prosecutors have charged a 22-year-old man with fatally stabbing his mother and teenage nephew in their Minneapolis home.

Ishmael Roberts was charged Wednesday in Hennepin County court with two counts of second-degree murder.

According to the criminal complaint, a witness awoke in the house and saw a man wearing a mask and dark clothing stabbing the woman. As he ran from the house to call 911 the witness says he heard the boy screaming. Police recovered a sheath for a sword at the scene.

The victims have not been identified, but the Star Tribune reports they are Roberts' mother, 57-year-old Beatrice Wilson, and her 14-year-old grandson Peter.

The victims were stabbed early Monday. Roberts was arrested in Iowa that night after authorities say he rolled Wilson's car and ran away.